Originally Posted by Asido
setComposite() is used to blend the source color with the destination color.i.e., Source is the one on which u draw and destination is the one that u draw. i.e., Source is similar to drawing board and destination is similar to the picture that u draw over the board.
AlphaComposite.getInstance(AlphaComposite.SRC_OVER ,0.20f) will perform the following action: Multiply the alpha value of the source with 0.20f and this is the alpha value of ur final image.
So,check the alpha value of ur source!!
AlphaComposite.SRC_OVER will work on the following logic:
If ur source is opaque,then it replaces the destination whereas if ur source is transparent,then ur destination remains unchanged.
If u have doubts, u can visit this site:
Blending Colors with AlphaComposite (Java Foundation Classes)
Hope this helps